DefineConstants overrides defined constants in all projects; use property to amend constants.

.github/workflows/build-ilspy.yml

@@ -95,7 +95,7 @@ jobs:
       run: |
         msbuild ILSpy.Installer.sln /t:Restore /p:Configuration="Release" /p:Platform="Any CPU"
         msbuild ILSpy.Installer.sln /p:Configuration="Release" /p:Platform="Any CPU"
-        msbuild ILSpy.Installer.sln /p:Configuration="Release" /p:Platform="Any CPU" /p:DefineConstants="ARM64"
+        msbuild ILSpy.Installer.sln /p:Configuration="Release" /p:Platform="Any CPU" /p:PlatformForInstaller="ARM64"
 
     - name: Build VS Extensions (for 2017-2019 and 2022)
       if: matrix.configuration == 'release'  

ILSpy.Installer/ILSpy.Installer.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
@@ -6,6 +6,10 @@
     <StartupObject>ILSpy.Installer.Builder</StartupObject>
   </PropertyGroup>
 
+  <PropertyGroup>
+    <DefineConstants>$(DefineConstants);$(PlatformForInstaller)</DefineConstants>
+  </PropertyGroup>
+
   <ItemGroup>
     <PackageReference Include="WixSharp" Version="1.22.0" />
     <PackageReference Include="WixSharp.wix.bin" Version="3.14.0" />